1. Field of the Invention
The present invention relates to a touch panel and a method of detecting a coordinate position.
2. Description of the Related Art
A touch panel is an input device usually provided in front of a display and capable of inputting data. As a user can directly input data based on information visually grasped by viewing the display through the touch panel, the touch panel is used in various ways.
A resistive touch panel or a capacitive touch panel is widely known.
For the resistive touch panel, transparent conductive layers are respectively formed on an upper conductive substrate and on a lower conductive substrate where the transparent conductive layers are positioned to face each other. When force is applied to a point of the upper conductive substrate to have the transparent conductive layers of the upper conductive substrate and the lower conductive substrate contact at the point where a potential gradient is generated on one of the transparent conductive layers, a coordinate position of the pushed point can be detected by reading an electric potential of the other of the transparent conductive layers.
Resistive touch panels mainly include a four-wire type, a five-wire type and a diode type. For the four-wire type, electrodes for applying potential gradients in an X-axis direction and in a Y-axis direction are respectively provided on one and the other of the upper conductive substrate and the lower conductive substrate (see patent document 1, for example). For the five-wire type, electrodes for applying potential gradients in both the X-axis direction and the Y-axis are provided on the lower conductive substrate, and the upper conductive substrate functions as a probe to read an electric potential (see patent document 2, for example). For the diode type, diodes are provided on the lower conductive substrate. Further, seven electrodes in total including two electrodes for applying a voltage and four electrodes for monitoring an electric potential provided on the lower conductive substrate and an electrode that functions as a probe to detect an electric potential provided on the upper conductive substrate are provided. Therefore, the diode type is also called a seven-wire type (see patent document 3, for example).
The capacitive touch panel detects a coordinate position of a touched point by detecting a current that flows through a transparent electrode or the like when a finger or the like touches or approaches the touch panel.
The capacitive touch panel detects a coordinate position by a capacitive coupling and therefore, the coordinate position can be detected just by touching, not necessarily pushing or pressing. However, when using an insulating material to touch the touch panel, the coordinate position cannot be detected. The resistive touch panel can detect a coordinate position even when an insulating material or the like is used for pushing the touch panel. However, it is necessary to push the touch panel with a certain force because the coordinate position can only be detected when the transparent conductive layer that functions as an upper resistive layer and the transparent conductive layer that functions as a lower resistive layer make contact.
A touch panel where a capacitive touch panel and a resistive touch panel are stacked so that both of the characteristics of the capacitive touch panel and the resistive touch panel are included is disclosed (see patent documents 4 or 5).